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Message-ID: <CAKv+Gu8dP33UYh-Vq1z-kXa+R_nXrFqpVOTsCW7qc2excrN4AA@mail.gmail.com>
Date: Wed, 12 Oct 2016 09:55:03 +0100
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: Mark Rutland <mark.rutland@....com>, Nick Kralevich <nnk@...gle.com>
Cc: kernel-hardening@...ts.openwall.com,
Laura Abbott <labbott@...oraproject.org>
Subject: Re: initcall randomization
(+ Nick)
On 12 October 2016 at 00:40, Mark Rutland <mark.rutland@....com> wrote:
> On Tue, Oct 11, 2016 at 07:28:46PM +0100, Ard Biesheuvel wrote:
>> vmalloc and ioremap calls will simply be served bottom up, which is
>> why the beginning of the vmalloc area mostly looks the same between
>> boots, i.e., all non-kaslr boots look identical, and all kaslr boots
>> look identical with little variation.
>>
>> I am aware that random vmalloc is a bad idea,
>
> I must confess ignorance here; what problems does random vmalloc pose in
> particular?
>
It has been attempted in Android, and resulted in vmalloc failures due
to fragmentation. I realize this may not apply to 64-bit ARM, though
(and I assume the Android example concerned 32-bit ARM)
>> hence my suggestion to perhaps randomize during the __init phase. I
>> must admit that this is simply me holding the randomization hammer and
>> looking for things that vaguely resemble nails, hence my request for
>> discussion rather than proposing patches.
>
> Do we have a particular threat model this helps with?
>
> Is it similar to that for SLUB freelist randomization?
>
> Do we have vmalloc area sepcific information leaks?
>
Well, that was my question as well. Given that it seemed like a good
idea for the Android guys at the time, I would assume yes
Nick?
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